A uniform electric field and a uniform magnetic field are acting along the same direction in a certain region. If an electron is projected along the direction of the fields with a certain velocity then (a) its velocity will increase (b) Its velocity will decrease (c) it will turn towards left of a direction of motion (d) it will turn towards right of direction of motion

Answer: (b). v ∥ B ⇒ magnetic force is zero, so no turning. Electric force on electron = -e E, opposite to v, so it decelerates. So the answer is (b) its velocity will decrease.

A uniform electric field and a uniform magnetic field are acting… | JEE Main 2005 (AIEEE)

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Moving Charge in a Magnetic Field

A uniform electric field and a uniform magnetic field are acting along the same direction in a certain region. If an electron is projected along the direction of the fields with a certain velocity then

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Answer: (b)

$\vec v \parallel \vec B \Rightarrow$ magnetic force is zero, so no turning.
Electric force on electron $= -e\vec E$ , opposite to $\vec v$ , so it decelerates.
So the answer is (b) its velocity will decrease.

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